Java HashMap遍历的两种方式

今天来搞一次HashMap 遍历的操作方式:

经过测试,方式一的效率要远高于方式二.,1000000条测试数据,第一种大概耗时20多秒,第二种耗时大概40多秒.所以,建议以后使用第一种方式.

直接上代码:

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

public class testHashMap {
	static Map<Object, Object> map;
	static long begin;
	static long end;

	public static void main(String[] args) {
		map = new HashMap<Object, Object>();
		for (int i = 0; i < 1000000; i++) {
			map.put("map" + i, i);
		}

		// 第一种:
		Iterator<Entry<Object, Object>> iter = map.entrySet().iterator();
		begin = System.currentTimeMillis();
		while (iter.hasNext()) {
			Entry<Object, Object> entry = iter.next();
			Object key = entry.getKey();
			Object val = entry.getValue();
			// System.out.println("["+key+","+val+"]");
		}
		end = System.currentTimeMillis();
		System.out.println("第一种,耗时" + (end - begin));

		// 第二种:

		Iterator<Object> iter1 = map.keySet().iterator();
		begin = System.currentTimeMillis();
		while (iter1.hasNext()) {
			Object key = iter1.next();
			Object val = map.get(key);
			// System.out.println("["+key+","+val+"]");
		}
		end = System.currentTimeMillis();
		System.out.println("第二种,耗时" + (end - begin));

	}

}